Interface materials are very important in high performance polymer solar cells (PSCs). Good interface materials not only enhance efficiency but also increase stable of organic solar cells. Poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), has been most commonly used as a interface layer in organic electronic devices. However, several problems of the PEDOT:PSS includes high acidity, hygroscopic properties, and inhomogeneous electrical properties, resulting in poor long-term stability. Graphene oxide (GO) can instead of PEDOT:PSS due to excellent optical transmittance and good stability. But the work function of commercial GO is only 4.9-5.0eV, that is not match with energy level of organic semiconductors, and limits the charge carrier extraction from the active to the electrodes. It is necessary to improve the work function of GO.
Recently, we introduce the chlorine in GO by photochemistry chlorination to fabricate the chlorinated GO (Cl-GO).The work function of GO is improved and can be tuned by controlling the time of photochemical chlorination. The morphology and the thickness of single-layer Cl-GO sheets are similar to that of single-layer GO sheets. Cl-GO with good optical transmission, high work functions, and excellent hole-extraction abilities have been demonstrated. The highest efficiency PBDTTT-C:PC71BM PSCs based on Cl-GO has been fabricated. The efficiency PSCs based on various polymer donors and fullerene derivatives acceptors have been successfully improved. Meanwhile, the different work function of Cl-GO have been used as anode interface layer, and we find the efficiency of PSCs have been greatly enhanced when the work function of Cl-GO is aligned closely with the highest occupied molecular orbital of polymer donors. This work provide scientific basis on matching the work function of interface layers with semiconductor energy level in organic solar cells.
Dong Yang, Lingyu Zhou, Wei Yu, Jian Zhang*, Can Li*, Advanced Energy Materials, 2014, DOI: 10.1002/aenm.201400591
http://onlinelibrary.wiley.com/doi/10.1002/aenm.201400591/abstract
